Diagnostic Aids
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- Using fuel other than ultra low sulfur content fuel will cause this DTC to set.
- A quality message may be present on the driver information center (DIC) with or without DTCs P20EE.
- A leak in the reductant system can be located by inspecting for a build-up of crystallized diesel exhaust fluid.
- Water in the reductant tank will cause this DTC to set. Multiple Reductant Fluid Quality tests will be necessary to heal the system once the reductant is replaced with fresh reductant.
- The NOx sensors cannot distinguish between NOx and liquid reductant. High NOx sensor 2 readings can be caused by reductant getting past the SCR catalyst. This can be the result of a degraded catalyst or a condition that causes excessive reductant on the SCR. After a DPF service regeneration, the SCR system is purged of excessive reductant. It is easier to evaluate if an SCR is compromised right after a service regeneration because it eliminates the extra reductant that the system was exposed to.
- During a DPF service regeneration, the SCR is too hot to reduce NOx effectively. NOx sensor 1 and NOx sensor 2 values should be relatively similar. NOx sensor 2 can be up to 30% higher than NOx sensor 1 in some cases.
- During a road test at operating temperature and highway speeds, the NOx sensor 2 should be 70% less than the NOx sensor 1 and transition in the same direction as the upstream sensor, but at a much lower magnitude. During a road test, you can collect transient data for NOx sensor 1 and NOx sensor 2. After a heavy acceleration followed by a tip out (zero pedal input), both sensors should go to zero while coasting down. If NOx sensor 2 does not go to zero shortly after NOx sensor 1, NOx sensor 2 is either faulty or the system is saturated with reductant. Performing this test during or shortly after a DPF regeneration prevents the system from being saturated with reductant.
- It is recommended that the following parameters are recorded every 2 minutes during and after each Reductant Fluid Quality Test and DPF Service Regeneration for reference as they may become necessary:
- NOx Sensor 1 NOx Concentration
- NOx Sensor 2 NOx Concentration
- EGT Sensor 1
- EGT Sensor 2
- EGT Sensor 3